1. Field of the Invention
The present invention relates to an apparatus for detecting a crack.
2. Description of the Related Art
Nondestructive testing (NDT) using a magnetic phenomenon is a method that is useful for detecting a surface defect in a structure, a backside defect near the surface of a structure, and an inner side defect near the surface of a structure. Using nondestructive testing, defects of large-scale plants and structures that are used in nuclear power generation, steam power generation and the chemical industry can be detected.
Conventional methods of detecting defects using the distribution of a magnetic field may be classified into a method of performing a two-dimensional (2D) scan using a single magnetic sensor, a method for performing a one-dimensional (1D) scan using sensors arranged in a single column, and a method of using sensors arranged in two dimensions.
The method of performing a 2D scan using a single magnetic sensor requires a longer period of time. The method for performing a 1D scan using sensors arranged in a single column requires separate scan equipment, and also requires that the scan equipment have high precision. The method of using sensors arranged in two dimensions has the advantage of measuring the distributions of a magnetic field at one time. However, the method of using sensors arranged in two dimensions has limited ability to quantitatively evaluate the size of a defect using the leakage of a magnetic field around the defect because single-axis magnetic sensors having magnetic sensitivity are arranged to perform the method.
Furthermore, a conventional method of measuring the distributions of the magnetic field of an object to be measured using tri-axial magnetic sensors limits its spatial resolution because a large number of wires are required.